1. Technical Field
The invention refers to a process for obtaining fatty acid alkyl esters, rosin acids and sterols from crude tall oil (CTO) which involves several esterification and distillation steps.
2. Background Art
The use of sterols to take control of cholesterol level in human nutrition body industry might increase a lot the demand of non-sterols. Consequently, separation process of sterols from Crude Tall Oil is highly interesting from the economical viewpoint, since this is one of the main source of sterols. Crude tall oil typically comes from the sulphate process employed in the manufacture of cellulose from wood. More particularly, the spent black liquor from the pulping process is concentrated until sodium salts (soaps) of various acids separate out and are skimmed off. The salts are acidified or decomposed with sulphuric acid so as to provide the crude tall oil.
Crude tall oil is refined mainly by vacuum distillation processes to separate the various compounds almost completely into rosin and fatty acid fractions. The current technology is based on distillation where the acids are fractionated in several columns. Using a first column to separate the more volatile fatty acids and rosin acids, from the less volatile materials, which include many of the unsaponifiable and neutral materials such as sterols and their esters. A second column is commonly designed to separate the more volatile fatty acids from the less volatile rosin acids. The tall oil fatty acids usually contain 1-5% rosin acids as by-products. This process usually ends up with a bottom that is currently called as “pitch”, where sterols, heavy hydrocarbons, wax alcohols are the main substances. Commercially, only fatty and rosin acids are produced. Pitch usually is used as a fuel. Due to the high distillation temperature there is significant sterols degradation. Also the most part of the free sterols are converted into esters. Tall oil pitch is a very viscous, dark product, which is rather difficult to handle. So far, there is no economic commercial process running to extract sterols from the pitch. From the state of the art a number of processes are known describing ways to extract sterols from CTO soaps using solvents and distillation processes prior to any acid splitting process, which theoretically could avoid sterols losses. See, for example, U.S. Pat. No. 6,107,456, U.S. Pat. No. 6,414,111, and U.S. Pat. No. 6,344,573. However, these processes are characterised by a high technical effort and were not reduced into practice for economical reasons.
A method of separating sterols from crude tall oil, wherein the sterols are not destroyed in the process, would be a useful invention in the chemical preparation industry. Therefore, the objective of this invention is to find out an economic process to separate the three main crude tall oil (CTO) components, fatty acids or their esters, rosin acids, and sterols, to get these commercially valuable products.